The invention relates to new antifouling marine paint compositions, that can be prepared totally free of organotin and yet give coatings having self-polishing properties.
Self-polishing antifouling coatings are known in the art. These coatings gradually dissolve so that a fresh anti-fouling paint surface is continuously revealed as moving seawater smoothes the surface of the coating. British Patent No. 1,1 24,297 discloses a film-forming copolymer containing a triorganotin comonomer which gives self-polishing antifouling coatings.
The known self-polishing antifouling paints use binders which are linear polymers containing side groups also called leaving groups. These leaving groups are released from the polymer by reaction with seawater, the resulting residual polymer being sufficiently dispersible or soluble in seawater is then swept away from the paint surface. This results in exposing a fresh layer of the binder able to undergo a similar reaction with seawater.
Coatings from such self-polishing paints retain their initial smoothness and can even become smoother from the action of relatively moving water.
These coatings generally contain a biocide that is active against fouling. The biocide is usually present as a pigment in the paint and/or released as a leaving group. The gradual thinning of the paint film controls the release of the biocide thus delivering the biocide from the surface at a relatively constant rate.
Most self-polishing paints employ binders that have triorganotin ester leaving groups. The triorganotin ester readily undergoes hydrolysis, releasing these leaving groups from the binder. The self-polishing action of these paints is dependent upon this hydrolysis, and the released triorganotin then provides a biocidal action. Examples of such paints can be found in British Pat. Nos. 1,124,297 and 1,457,590, in European Patent Application Nos. 51,930, 151,809 and 218,573, and in Japanese Patent Application Nos. 231061/61 and 231062/61. British Patent Application No. 2,159,827 discloses similar paints with diorganotin leaving groups.
Many countries are introducing new stringent water quality programs, some of which call for a phased reduction in the organotin content of marine paints. There are also cost advantages in replacing the expensive triorganotin comonomers. Examples of low or no organotin content marine paints are found in European Pat. No. 69,559 which discloses a copolymer prepared from quinolinyl esters of olefinically unsaturated carboxylic acid with other olefinically unsaturated comonomers, and International Patent Application No. WO 84/0291 5 which suggests a wide range of organic leaving groups for use in antifouling paint binders. It has been found, however, that the binder in these type of marine paints generally does not hydrolyze quickly enough in seawater; and, therefore, these paints are not adequately self polishing.
European Patent Application No. 204,444, also discloses a marine paint that doesn't require organotin. This patent application discloses a binder that is a hydrolyzable polymer prepared with a triaryl(methyl) methacrylate comonomer. The esterification reactions with these comonomers, however, are more difficult than with triorganotin comonomers; therefore, the hydrolysis will be more difficult. Since the hydrolysis is difficult, satisfactory marine paint cannot be prepared using these binders with what is known today.
International Patent Application No. WO 86/02660 discloses certain polycarboxylic polymers, substantially non-ionic, which are changed by reaction with seawater into polycarboxylate polymers sufficiently dispersible or soluble. These polymers do not require organotin and can be used as binders for self-polishing antifouling paints. However, the resulting coatings swell when immersed, and the paints, that typically contain ZnO or cuprous oxide as the toxic agent, gel on storage. Both of these problems prevent the use of these binders in self-polishing antifouling marine paints.
There is therefore a need for organotin-free self-polishing antifouling marine paints which do not have these drawbacks.